Back Button Focus Explained
Back button focus is one of the most undervalued custom functions on your digital camera. It can mean the difference between capturing a fast action and completely missing it. Lucky for us, it’s easy to set up for underwater photography.
Handling yourself and your dive gear while shooting underwater photos is challenging in itself, but we are also shooting our camera through a housing. Something as simple as half-depressing a shutter can quickly turn into a challenging task, as we lose a lot of the feel of the shutter button.
This challenge can quickly escalate underwater, if for example, you fire the shot a second too early by accident, then shoot again, but find that your strobes are still recycling… and you have a black frame.
This is where back button focus becomes important.
Back Button Focus for Underwater Photographers
How does Back Button Focus help?
This function allows you separate your camera’s autofocus from from the shutter release. When combined with continuous autofocus, you are able to track a subject and then shoot the image at just the right moment, minimizing lens hunting, pre-firing, and other situations that result in missing a great photo moment.
When shooting ambient light without strobes, we can choose an automatic shooting mode so that the camera determines the best image exposure, leaving us to focus on framing and composition.
How do I know if my camera has back button focus capability?
Most compact, mirrorless and DSLR cameras will allow you to shoot in this method. As a bonus most mirrorless and DSLR housings have controls designed to help make back button focus more ergonomic when shooting underwater with a tray and handle system.
When should I use back button focus?
This is a matter of personal preference. I have actually added the button customizations to my custom camera menu so that I can quick re-assign buttons depending whether I’d like to use back button focus or not.
Generally, I find myself using back button focus for wide-angle shooting, while switching to half-depress AF activation for macro shooting.
One thing is for sure: you will benefit from using this technique for fast action shooting, as outlined in the video tutorial towards the beginning of the article.